Reinforced window member and method of manufacturing the same

ABSTRACT

A method of manufacturing a window member includes performing a first reinforcement operation including performing a first ion-exchange treatment on an initial window member. The first ion-exchange treatment includes applying ion salts at a temperature equal to or greater than a first temperature of about 500° C. A stress relief operation includes performing a heat treatment and/or a salt treatment on the initial window member to which the first reinforcement operation is performed. A second reinforcement operation includes performing a second ion-exchange treatment on the initial window member to which the stress relief operation is performed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. Non-Provisional Patent application is a Division of co-pendingU.S. Pat. Application Serial No. 15/926,146, filed on Mar. 20, 2018,which claims priority under 35 U.S.C. §119 to Korean Patent ApplicationNo. 10-2017-0048080, filed on Apr. 13, 2017 and Korean PatentApplication No. 10-2017-0136116, filed on Oct. 19, 2017, the contents ofwhich are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to a window member, and moreparticularly, to a reinforced window member and a method ofmanufacturing the reinforced window member.

DISCUSSION OF THE RELATED ART

Often, electronic devices with display screens include a window memberthrough which the display screen may be seen. An accommodation membermay house the electronic device, the display screen and the windowmember.

The window member protects the display screen and the electronic deviceand provides a user with an active region though which am image may beobserved and a touch inputs may be received. Accordingly, the userprovides an input to the electronic device or receives informationgenerated by the electronic device through the window member. Inaddition, the electronic device is protected from external impacts bythe window member.

SUMMARY

A method of manufacturing a window member includes performing a firstreinforcement operation including performing a first ion-exchangetreatment on an initial window member. The first ion-exchange treatmentincludes applying ion salts at a temperature equal to or greater than afirst temperature of about 500° C. A stress relief operation includesperforming a heat treatment and/or a salt treatment on the initialwindow member to which the first reinforcement operation is performed. Asecond reinforcement operation includes performing a second ion-exchangetreatment on the initial window member to which the stress reliefoperation is performed.

A method of manufacturing a window member includes performing a firstreinforcement operation including performing a first ion-exchangetreatment on an initial window member, thereby giving the initial windowmember a first surface compressive stress and a first depth ofcompression. A stress relief operation includes performing a heattreatment or a salt treatment on the initial window member to which thefirst reinforcement operation is performed, thereby decreasing the firstsurface compressive stress to a second surface compressive stress andthereby changing the first depth of compression to a second depth ofcompression different from the first depth of compression. A secondreinforcement operation includes performing a second ion-exchangetreatment on the initial window member to which the stress reliefoperation is performed, thereby increasing the second surfacecompressive stress to a third surface compressive stress.

A window member includes a base including a first surface and a secondsurface facing the first surface in a first direction. The base has athickness defined in the first direction. First ion salts aredistributed in the base and each of the first ion salts has a first ionradius. Second ion salts are distributed in the base and each of thesecond ion salts has a second ion radius greater than the first ionradius. A variation in compressive stress according to a depthincreasing along the first direction from the first surface of the baseforms a first plot, and the first plot includes a point at which anabsolute value of a slope is smaller than about 2 MPa/µm in a depthrange in which the compressive stress is greater than about 0 MPa/µm.

A window member includes a first surface and a second surface facing thefirst surface. The window member has a thickness defined in a firstdirection between the first surface and the second surface. The windowmember has a compressive stress smaller than about 150 MPa on the firstsurface, and has a compressive stress graph varied depending on a depthincreasing along the first direction from the first surface. Thecompressive stress graph includes a first plot at a depth equal to orsmaller than a transition point and a second plot at a depth greaterthan the transition point. The first plot has an average slope equal toor greater than about -200 MPa/µm and equal to or smaller than about -40MPa/µm. The second plot has an average slope different from the firstplot. The transition point is greater than about 15 µm.

A method of manufacturing a window member includes performing a firstreinforcement operation including an ion-exchange treatment operationthat exposes an initial window member to a first reinforcementenvironment at a first temperature equal to or greater than about 500°C. The first reinforcement environment includes a first ion salt. Asecond reinforcement operation includes providing the first-reinforcedinitial window member to a second reinforcement environment at a secondtemperature smaller than about 500° C. thereby performing anion-exchange treatment on the first-reinforced initial window member.The second reinforcement environment includes a second ion salt.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present disclosure and many of theattendant aspects thereof will become readily apparent by reference tothe following detailed description when considered in conjunction withthe accompanying drawings wherein:

FIG. 1A is an assembled perspective view illustrating an electronicdevice according to an exemplary embodiment of the present disclosure;

FIG. 1B is an exploded perspective view illustrating the electronicdevice shown in FIG. 1A;

FIG. 2A is a graph illustrating a stress profile as a function of adepth of a window member according to an exemplary embodiment of thepresent disclosure;

FIG. 2B is a graph illustrating a stress profile as a function of adepth of a window member according to a comparative embodiment;

FIG. 3A is an assembled perspective view illustrating an electronicdevice according to an exemplary embodiment of the present disclosure;

FIG. 3B is an exploded perspective view illustrating the electronicdevice shown in FIG. 3A;

FIG. 4 is a flowchart illustrating a method of manufacturing a windowmember according to an exemplary embodiment of the present disclosure;

FIGS. 5A to 5G are cross-sectional views illustrating a method ofmanufacturing a window member according to an exemplary embodiment ofthe present disclosure;

FIG. 6 is a graph illustrating a variation in stress of a window memberaccording to an exemplary embodiment of the present disclosure;

FIGS. 7A and 7B are graphs illustrating a variation of a compressivestress as a function of a depth of a window member according to anexemplary embodiment of the present disclosure;

FIGS. 8A and 8B are graphs illustrating a variation of a compressivestress as a function of a depth of a window member according to anexemplary embodiment of the present disclosure;

FIGS. 9A and 9B are graphs illustrating a variation of an ionconcentration as a function of a depth of a window member according toan exemplary embodiment of the present disclosure;

FIGS. 10A and 10B are graphs illustrating a variation of an ionconcentration as a function of a depth of a window member according toan exemplary embodiment of the present disclosure;

FIG. 11A is a flowchart illustrating a method of manufacturing a windowmember according to an exemplary embodiment of the present disclosure;

FIG. 11B is a flowchart illustrating a portion of the method ofmanufacturing the window member of FIG. 11A;

FIG. 12 is a graph illustrating a compressive stress as a function of adepth of a window member according to an exemplary embodiment of thepresent disclosure;

FIG. 13 is a graph illustrating a compressive stress as a function of adepth of a window member according to an exemplary embodiment of thepresent disclosure; and

FIGS. 14A and 14B are graphs illustrating a compressive stress as afunction of a depth of a window member according to an exemplaryembodiment of the present disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

In describing exemplary embodiments of the present disclosureillustrated in the drawings, specific terminology is employed for sakeof clarity. However, the present disclosure is not intended to belimited to the specific terminology so selected, and it is to beunderstood that each specific element includes all technical equivalentswhich operate in a similar manner.

Hereinafter, the present invention will be explained in detail withreference to the accompanying drawings.

FIG. 1A is an assembled perspective view illustrating an electronicdevice DS according to an exemplary embodiment of the presentdisclosure. FIG. 1B is an exploded perspective view illustrating theelectronic device DS shown in FIG. 1A. The electronic device DS,according to exemplary embodiments of the present disclosure, will bedescribed in detail with reference to FIGS. 1A and 1B.

Referring to FIG. 1A, the electronic device DS may have athree-dimensional shape with a predetermined thickness in a firstdirection DR1. The electronic device DS may include an active region ARand a peripheral region BR, which may surround the active region AR onat least one side thereof. The active region AR and the peripheralregion BR may share a plane defined by a second direction DR2 and athird direction DR3, each of which may be substantially perpendicular tothe first direction DR1.

The active region AR may be a region in which input and/or outputfunctions of the electronic device DS are performed. According to anexemplary embodiment of the present disclosure, the electronic device DSmay be, but is not limited to being, a display device. Accordingly, theactive region AR displays an image IM when the electronic device DS isactivated.

According to an exemplary embodiment of the present invention, theactive region AR may be a region used to sense an external touch orambient light after the electronic device DS is activated. Accordingly,the active region AR may be operated in various regions depending oncomponents included in the electronic device DS and the presentinvention should not be limited to any one of the particular examplesfor ways in which the electronic device DS is utilized through theactive region.

The peripheral region BR is disposed adjacent to the active region AR.For example, the peripheral region BR may have a shape surrounding anedge of the active region AR. However, the peripheral region BR might beadjacent to only a portion of the edge of the active region AR.Alternatively, the peripheral region BR may be omitted from theelectronic device DS all together.

Referring to FIGS. 1A and 1B, the electronic device DS includes a windowmember 100, such as a window, a display member 200, such as a display,and an accommodation member 300, such as a frame or housing. Theaccommodation member 300, the display member 200, and the window member100 may be sequentially arranged in the first direction DR1.

The window member 100 may be one of several external members of theelectronic device DS. The window member 100 is coupled with theaccommodation member 300 to define an inner region in which innercomponents are disposed. The inner components may be protected fromexternal impacts and environmental contaminants within the inner region.For example, the window member 100 may define a front surface of theelectronic device DS.

The window member 100 may include a rigid material. For example, thewindow member 100 may include a glass or plastic material. Accordingly,the window member 100 may protect the inner components of the electronicdevice DS from external impacts and environmental contaminants such asliquids, vapors, and reactive substances.

The window member 100 may be strengthened with the inclusion of ionsalts. The ion salts may include a monovalent alkali ion. For example,the ion slats may include a sodium ion and a potassium ion. This will bedescribed in detail later.

The window member 100 may include a first region 100-AR and a secondregion 100-BR, which are arranged on the plane defined by the seconddirection DR2 and the third direction DR3.

The first region 100-AR may be an optically transparent region. Thefirst region 100-AR transmits the image IM generated by the displaymember 200 to allow the image IM to be recognized by a user. The activeregion AR may be substantially defined by and aligned with the firstregion 100-AR.

The second region 100-BR is disposed adjacent to the first region100-AR. The second region 100-BR has a lower optical transmittance thanthat of the first region 100-AR, thereby making the second region 100-BRharder to see through than the first region 100-AR. The first region100-AR may have a shape defined by the second region 100-BR. Accordingto an exemplary embodiment of the present invention, the second region100-BR may be omitted from the electronic device DS.

The window member 100 may include a first (upper) surface US and asecond (lower) surface LS separated from the first surface US in thefirst direction DR1 on the plane defined by the second direction DR2 andthe third direction DR3. The first surface US may be substantiallyparallel to the second surface LS.

The first surface US may define the front surface of the electronicdevice DS. The first surface US corresponds to a surface exposed to theuser who uses the electronic device DS.

The second surface LS may be a surface facing the display member 200.The second surface LS is not exposed to the outside of the electronicdevice DS in the assembled perspective view shown in FIG. 1A.

The window member 100 may have a thickness TH defined in the firstdirection DR1. The thickness TH may correspond to a degree of separationbetween the first surface US and the second surface LS.

The window member 100 may be thin. For example, the thickness TH of thewindow member 100 may be equal to or smaller than about 0.5 mm. Althoughthe window member 100 has the thickness of about 0.5 mm, the windowmember 100 may be sufficiently strong to withstand external impacts.This will be described in detail later. Since the electronic device DS,according to exemplary embodiments of the present invention, includesthe thin window member 100, the electronic device DS may be slim,lightweight, and highly optically transparent, etc.

As discussed above, the window member 100 may be both thin and strong.Accordingly, the electronic device DS may be made relatively slim andresistant to damage caused by external impacts. This will be describedin detail later.

The display member 200 may be disposed between the window member 100 andthe accommodation member 300. The display member 200 generates the imageIM. The image IM generated by the display member 200 may provide theuser with information.

The display member 200 may include a base layer 210 and a device layer220. The base layer 210 may include an insulating material. For example,the base layer 210 may be a glass substrate, a plastic substrate, or astacked film including an organic layer and/or an inorganic layer, butthe base layer is not limited to these components. For example, the baselayer 210 according to the present exemplary embodiment may includevarious components and should not be limited to any one embodiment.

The device layer 220 may include various electrical devices activated inresponse to electrical signals. For example, the device layer 220 mayinclude display devices to generate the image IM. For example, thedevice layer 220 may include an organic light emitting device, anelectrowetting device, a liquid crystal capacitor, or an electrophoreticdevice.

According to an exemplary embodiment of the present invention, thedevice layer 220 may include a sensor device, such as a touch sensor, anoptical sensor, etc. The device layer 220 may, for example, includevarious devices for performing various functions of the electronicdevice DS.

The accommodation member 300 may be one of the external members of theelectronic device DS. The accommodation member 300 is coupled with thewindow member 100 to seal and protect the inner components from theexternal environment. For example, the accommodation member 300 maydefine a rear surface of the electronic device DS.

The accommodation member 300 may include a bottom portion 310 (e.g.backplate) and a sidewall portion 320. The bottom portion 310 and thesidewall portion 320 may define a predetermined inner space SP orcavity. The display member 200 may be accommodated within the innerspace SP.

The bottom portion 310 may be substantially parallel to the planedefined by the second direction DR2 and the third direction DR3.However, the bottom portion 310 may alternatively be curved and/or maycontain one or more openings or protruding features. The bottom portion310 may overlap with at least the display member 200 when viewed in aplan view. The bottom portion 310 may have an area equal to or greaterthan an area of the display member 200.

The sidewall portion 320 is connected to the bottom portion 310 andextends from the bottom portion 310 in substantially the first directionDR1, although the sidewall portion 320 may alternatively be somewhatrounded so as to bulge outwardly. The sidewall portion 320 may definethe thickness in the first direction DR1 of the electronic device DS.The sidewall portion 320 may surround an edge of the display member 200in the assembled perspective of FIG. 1A.

The electronic device DS may further include various additionalcomponents accommodated in the inner space SP. For example, theelectronic device DS may further include a component supplying a powerto the display member 200, a component coupling the window member 100with the display member 200, and a component coupling the display member200 with the accommodation member 300. The electronic device DS may beprovided in various structures including various components and shouldnot be limited to a specific structures described herein as examples.

FIG. 2A is a graph illustrating a stress profile as a function of adepth of a window member according to an exemplary embodiment of thepresent disclosure, and FIG. 2B is a graph illustrating a stress profileas a function of a depth of a window member according to a comparativeembodiment. FIG. 2A relates to the properties of the window member 100shown in FIG. 1B.

Referring to FIGS. 2A and 2B, a level of stress occurring in the windowmember 100 may vary depending on a depth. The depth may be defined as adistance between the first surface US (refer to FIG. 1B), correspondingto one surface of the surfaces of the window member 100, and a pointthat is spaced apart from the first surface US toward a center of thethickness of the window member 100 by a predetermined separationdistance in the first direction DR1 (refer to FIG. 1B). Similarly, thedepth may be defined as a distance between one surface among thesurfaces of a comparative embodiment and a point that is spaced apartfrom the one surface toward a center of a thickness of the comparativeembodiment.

The stress may be a stress at a point spaced apart from the surface ofthe window member 100 in a thickness direction of the window member 100by a corresponding depth. Similarly, the stress may be a stress existingat a corresponding point in the comparative embodiment.

In FIGS. 2A and 2B, a type of the stress, which occurs in the windowmember and is caused by a depth, has been represented as a compressivestress.

As shown in FIGS. 2A and 2B, the compressive stress at a point at whichthe depth is zero (0) in the window member 100, e.g., at the pointcorresponding to the surface of the window member 100, may be referredto as a “surface compressive stress”. In addition, in the window member100, a point at which the compressive stress is zero (0) may be referredto as a “depth of compression”. Hereinafter, a compressive stressbehavior of the window member according to an exemplary embodiment ofthe present disclosure will be described in detail with reference toFIGS. 2A and 2B.

As shown in FIG. 2A, a compressive stress graph PL of the window member100, according to an exemplary embodiment of the present disclosure,shows the surface compressive stress equal to about 800 MPa, and thedepth of compression equal to about 80 micrometers.

As shown in FIG. 2B, according to a graph PL-R of the comparativeembodiment, the surface compressive stress, which indicates thecompressive stress at the point at which the depth is zero (0), is about650 MPa, and the depth of compression is about 70 micrometers at a pointat which the compressive stress is zero (0). For example, the windowmember 100, according to an exemplary embodiment of the presentdisclosure, has a higher surface compressive stress and a greater depthof compression than those of the comparative embodiment.

Referring to FIGS. 2A and 2B, when the graph PL of the presentdisclosure is compared to the graph PL-R of the comparative embodiment,the graph PL may be divided into a section with a large slope and asection with a small slope in a depth range equal to or smaller than thedepth of compression. According to exemplary embodiments of the presentinvention, a magnitude of the slope is determined based on an absolutevalue.

For example, the graph PL of the present disclosure has a larger slopethan that of the graph PL-R of the comparative embodiment in the depthrange smaller than about 15 micrometers and has a smaller slope thanthat of the graph PL-R of the comparative embodiment in the depth rangeequal to or greater than about 15 micrometers.

Meanwhile, the graph PL of the present disclosure may include a point atwhich an absolute value of the slope is smaller than about 2 MPa/µm inthe depth range equal to or smaller than the depth of compression. Forexample, a first slope SL1 is about 1 MPa/µm.

The graph PL-R of the comparative embodiment may include points at whichabsolute values of the slope is equal to or greater than about 2 MPa/µmin the depth range equal to or smaller than the depth of compression.For example, a second slope SL2 is about 2.62 MPa/µm.

The graph PL of the present disclosure may include a point at which theslope is zero (0). Accordingly, as shown in FIG. 2A, the graph PL of thepresent disclosure may include a peak point PK that is upwardly convex.According to some exemplary embodiments of the present invention, thegraph PL of the present disclosure may have various shapes as long asthe graph PL includes the point at which the absolute value of the slopis smaller than about 2 MPa/µm, and the graph PL of the presentdisclosure should not be limited to any one embodiment.

The graph PL, according to exemplary embodiments of the presentdisclosure, shows the surface compressive stress being higher than thatof the graph PL-R of the comparative embodiment and quickly reaches thelow compressive stress in the low depth due to the high slope. Inaddition, the graph PL, according to exemplary embodiments of thepresent disclosure, has the higher depth of compression than that of thegraph PL-R of the comparative embodiment, but has the lower slope thanthat of the graph PL-R, thereby inducing a reduction of the compressivestress.

The stress applied to the window member 100 due to the compressivestress may correspond to an area defined by the graph PL. The stressapplied to the window member 100 due to the compressive stress may berelieved by a negative compressive stress, e.g., a tensile force, whichis generated in a depth range equal to or greater than the depth ofcompression. In this case, an inner tension formed to relieve the stressapplied to the window member 100 may be referred to as a centraltension.

As the stress applied to the window member 100 increases, the centraltension generated in the depth range equal to or greater than the depthof compression increases. In this case, when the thickness of the windowmember 100 is reduced, the depth range equal to or greater than thedepth of compression is not secured by a sufficient length. As a result,the central tension may rapidly increase, and the durability of thewindow member 100 may be lowered.

The window member 100, according to exemplary embodiments of the presentdisclosure, has the graph PL including the section with the larger slopeand the section with the smaller slope than those of the comparativeembodiment. Accordingly, although the graph PL has the highercompressive stress and the higher depth of compression than those of thegraph PL-R of the comparative embodiment, an area smaller than an areaformed by the graph PL-R of the comparative embodiment may be formed bycontrolling the slope.

Accordingly, the window member 100 may substantially simultaneously havethe high depth of compression and the low central tension, and thus thewindow member 100 may me highly reliable and durable and provideadequate stability and protection even though the window member 100 isrelatively thin. The window member 100, according to exemplaryembodiments of the present disclosure, may be thin while beingreinforced, and thus the window member 100 may contribute to thethinning of the electronic device DS.

FIG. 3A is an assembled perspective view illustrating an electronicdevice DS-1 according to an exemplary embodiment of the presentdisclosure, and FIG. 3B is an exploded perspective view illustrating theelectronic device DS-1 shown in FIG. 3A. Hereinafter, the electronicdevice DS-1 will be described in detail with reference to FIGS. 3A and3B. In FIGS. 3A and 3B, the same reference numerals may denote the sameelements in FIGS. 1A to 2B, and thus to the extent that description isomitted, it may be assumed that the omitted description is at leastsimilar to that of the corresponding elements already discussed.

Referring to FIG. 3A, the electronic device DS-1 may include an activeregion AR-1 and a peripheral region BR-1. The active region AR-1 mayhave a curved shape in a space defined by a first direction DR1, asecond direction DR2 crossing the first direction DR1, and a thirddirection DR3 crossing the first direction DR1.

The peripheral region BR-1 is disposed adjacent to the active regionAR-1. The peripheral region BR-1 may have a curved shape correspondingto that of the active region AR-1.

An image is displayed through the active region AR-1. For example, afirst image IM1 and a second image IM2 may be displayed through theactive region AR-1. The first image IM1 is displayed through a planedefined by the second direction DR2 and the third direction DR3 andprovided to the first direction DR1. The second image IM2 is displayedthrough a plane defined by the first direction DR1 and the seconddirection DR2 and provided to the third direction DR3.

The electronic device DS-1, according to exemplary embodiments of thepresent disclosure, may display the image toward various directionsthrough the active region AR-1 having the curved shape. Accordingly, theelectronic device DS-1 may provide the user with various ways of usingthe electronic device DS-1.

As shown in FIGS. 3A and 3B, the electronic device DS-1 may include awindow member 100-1, a display member 200-1, and an accommodation member300-1. The window member 100-1 may have the curved shape bent downwardfrom the plane defined by the second direction DR2 and the thirddirection DR3.

The window member 100-1 may include a first region 100-AR1 and a secondregion 100-BR1. The first region 100-AR1 may be substantially parallelto the plane defined by the second direction DR2 and the third directionDR3. The first region 100-AR1 may correspond to the active region AR-1.

The second region 100-BR1 may be a region bent downward from the firstregion 100-AR1. The second region 100-BR1 may be substantially parallelto the plane defined by the first direction DR1 and the second directionDR2. The second region 100-BR1 may correspond to the peripheral regionBR-1.

The window member 100-1 may have the same structure and function asthose of the window member 100 (refer to FIG. 1B) except that the windowmember 100-1 has the curved shape. Accordingly, to the extent thatadditional description is omitted, it may be assumed that the omitteddescription is at least similar to that of the corresponding windowmember 100 already discussed.

The display member 200-1 may be disposed between the window member 100-1and the accommodation member 300-1. The display member 200-1 may havethe curved shape bent downward from the plane defined by the seconddirection DR2 and the third direction DR3.

The display member 200-1 includes a base layer 210-1 and a device layer220-1. The base layer 210-1 and the device layer 220-1 may have thecurved shape bent downward from the plane defined by the seconddirection DR2 and the third direction DR3.

Since the device layer 220-1, according to exemplary embodiments of thepresent disclosure, has the curved shape, first and second images IM1and IM2 may be generated. These images may be displayed in differentdirection, with the first image IM1 being displayed substantially in theDR1 direction and the second image IM2 being displayed substantially inthe D3 direction. Accordingly, the display member 200-1 may provide theimages toward various directions and increase the usability of theelectronic device DS-1.

The accommodation member 300-1 is disposed under the display member200-1. The accommodation member 300-1 is coupled with the window member100-1 to define a portion of the exterior of the electronic device DS-1and protect inner components of the electronic device DS-1. Theaccommodation member 300-1 has a shape that may be coupled with variousshapes of the display member 200-1, and thus the display member 200-1and other additional components may be accommodated in the electronicdevice DS-1.

As described above, the electronic device DS-1, according to exemplaryembodiments of the present disclosure, includes the window member 100-1having the curved shape, and thus the display member 200-1 havingvarious shapes and other electrical components may be protected fromcontamination by the external environment. In addition, since the windowmember 100-1 may secure a mechanical strength while having variousshapes, the reliability of the electronic device DS-1 may be increased.

FIG. 4 is a flowchart illustrating a method of manufacturing a windowmember according to an exemplary embodiment of the present disclosure.FIGS. 5A to 5G are cross-sectional views illustrating a method ofmanufacturing a window member according to an exemplary embodiment ofthe present disclosure. For the convenience of explanation, FIGS. 5A to5G show a variation on a cross-section defined by the first directionDR1 and the third direction DR3.

Hereinafter, the manufacturing method of the window member will bedescribed in detail with reference to FIGS. 4 and 5A to 5G. In FIGS. 4and 5A to 5G, the same reference numerals denote the same elements inFIGS. 1A to 3B, and thus to the extent that description is omitted, itmay be assumed that the omitted description is at least similar to thatof the corresponding elements already discussed.

Referring to FIG. 4 , the method of manufacturing the window member 100,according to exemplary embodiments of the present disclosure may includea first reinforcement operation S100, a stress relief operation S200,and a second reinforcement operation S300.

The first reinforcement operation S100 may include an ion exchangeoperation. The manufacturing method of the window member 100, accordingto exemplary embodiments of the present disclosure, may form a firstwindow member 100-S1 from an initial window member 100-I through thefirst reinforcement operation S100.

FIGS. 5A to 5C may correspond to the first reinforcement operation S100.The first reinforcement operation S100 may be an operation thatreinforces the initial window member 100-I.

The initial window member 100-I may include a rigid insulatingsubstrate. For example, the initial window member 100-I may be a glasssubstrate.

For example, as shown in FIG. 5A, the initial window member 100-I mayinclude a medium MD and a plurality of sodium ions (Na⁺). The sodiumions (Na⁺) may be distributed (e.g. dissolved or otherwise mixed orsuspended) within the medium MD (solvent or another carrier material).

The initial window member 100-I may be a glass substrate from whichlithium oxide (Li₂O), boric oxide (B₂O₃), or phosphorus pentoxide (P₂O₅)is removed. The initial window member 100-I, according to exemplaryembodiments of the present disclosure, may include a glass substrateformed of various materials without being limited to a specificmaterial.

The first reinforcement operation S100 may include an ion exchangetreatment. Accordingly, the first reinforcement operation S100 may treatthe initial window member 100-I with a salt containing predeterminedionic salts.

In particular, as shown in FIGS. 5B and 5C, a plurality of potassiumions (K⁺) is provided to the initial window member 100-I to form thefirst window member 100-S1. The first window member 100-S1 may includethe medium MD and the sodium ions (Na⁺) and the potassium ions (K⁺),which are distributed in the medium MD. The potassium ions (K⁺) may beions substituted for the sodium ions (Na⁺) distributed in the medium MD.

The potassium ions (K⁺) may be provided in a variety of ways. Forexample, the potassium ions (K⁺) may be provided in a state of ionicliquid.

For example, the initial window member 100-I is exposed to a molten saltto provide the potassium ions (K⁺) existing in the molten salt to theinitial window member 100-I. The molten salt may be a mixed salt.

For example, the molten salt may be a mixed salt in which sodium nitrate(NaNO₃) is mixed with potassium nitrate (KNO₃). At least a portion ofthe potassium ions (K⁺) existing in the molten salt infiltrates into theinitial window member 100-I to be substituted for the sodium ions (Na⁺)in a one-to-one correspondence.

In this case, the molten salt may be provided to the first surface USand the second surface LS. Since the molten salt is provided in a liquidstate, the surface of the initial window member 100-I may be exposed tothe potassium ions (K⁺). The potassium ions (K⁺), according to exemplaryembodiments of the present disclosure, may be provided in variousmethods, and the method of providing the potassium ions (K⁺) should notbe limited to any one embodiment.

For example, the ions provided to the initial window member 100-I may beprovided in various embodiments as long as the ions are able to besubstituted for the sodium ions (Na⁺). For example, the ions provided tothe initial window member 100-I may be monovalent positive ions havingthe same outermost electron number as the sodium ions (Na⁺).

The potassium ions (K⁺) have a relatively large ion radius compared tothe sodium ions (Na⁺). Accordingly, the potassium ions (K⁺) larger thanthe sodium ions (Na⁺) are provided to positions at which the sodium ions(Na⁺) are placed, and the compressive stress is generated with respectto the medium MD.

The compressive stress provided by the potassium ions (K⁺) may cause thesurface compressive stress on the surface, i.e., the first surface USand the second surface LS, of the initial window member 100-I. Thus, thefirst window member 100-S1 may have a predetermined surface compressivestress.

The potassium ions (K⁺) injected into the initial window member 100-Ifrom the outside of the initial window member 100-I may enter theinitial window member 100-I from the surface thereof to a predetermineddepth. The predetermined depth may indicate a separation distancebetween the first surface US or the second surface LS and a potassiumion farthest apart from the first surface US or the second surface LSamong the potassium ions (K⁺) in the first direction DR1. Accordingly,the first window member 100-S1 may have a predetermined depth ofcompression. As described above, the depth of compression may correspondto the depth at which the compressive stress becomes zero (0).

A temperature at the first reinforcement operation S100 is carried outmay be related to a distortion point of the initial window member 100-I.The first reinforcement operation S100 may be carried out at atemperature of about ±20° C. with respect to a temperature that is lowerthan the distortion point by about 50° C. The distortion point may bechanged depending on a material or a crystal structure of the initialwindow member 100-I.

For example, in a case that the distortion point of the initial windowmember 100-I is about 580° C., the first reinforcement operation S100may be carried out at a temperature of about 500° C. or above. The firstreinforcement operation S100, according to exemplary embodiments of thepresent disclosure, performs the ion exchange at a relatively hightemperature, and thus the potassium ions (K⁺) may infiltrate into theinitial window member 100-I, and the ion exchange may be active.

The temperature of the first reinforcement operation S100, according tothe present disclosure, may be higher than a temperature range of aslow-cooling temperature for a manufacturing method of a conventionalreinforced glass. In the case that the first reinforcement operationS100 is performed on the initial window member 100-I having thedistortion point of about 580° C. at the temperature equal to or lowerthan about 500° C., the depth of compression of the initial windowmember 100-I may be lower than that at the temperature higher than 500°C. with respect to the same exposure time. In order to increase thecompressive stress or the depth of compression, the exposure time isincreased. Accordingly, a process efficiency is deteriorated, and amanufacturing cost increases.

Then, as shown in FIG. 4 , the stress relief operation S200 may beperformed. The stress relief operation S200 may correspond to FIGS. 5Dand 5E. The stress relief operation S200 relieves the compressive stressof the initial window member (hereinafter, referred to as a “firstwindow member”) 100-S1, which is first-reinforcement treated, to form aninitial window member (hereinafter, referred to as a “second windowmember”) 100-S2 that is stress-relief treated. The second window member100-S2 may have the compressive stress lower than that of the firstwindow member 100-S1.

The manufacturing method of the window member, according to exemplaryembodiments of the present disclosure, may control a movement of thepotassium ions (K⁺) through the stress relief operation S200. Forexample, referring to FIGS. 5D and 5E, the potassium ions (K⁺) may moveto a center portion CTR in thickness direction of the first windowmember 100-S1 in the stress relief operation S200.

When the potassium ions (K⁺) providing the compressive stress move tothe center portion CTR from the first and second surfaces US and LS,influences exerted on the first and second surfaces US and LS by thesources of the surface compressive stress may be reduced. Accordingly,the surface compressive stress measured at each of the first and secondsurfaces US and LS of the second window member 100-S2 may be lower thanthat of the first window member 100-S1. In this case, the surfacecompressive stress of the second window member 100-S2 may be smallerthan about 150 MPa.

When the potassium ions (K⁺) providing the compressive stress move tothe center portion CTR from the first and second surfaces US and LS, apoint with a compressive stress greater than the surface compressivestress may exist inside the second window member 100-S2. Since thepotassium ions (K⁺) providing the compressive stress move to be adjacentto the center portion CTR through the stress relief operation S200, apoint having a maximum compressive stress may move to the center portionCTR from the first and second surfaces US and LS.

In this case, the potassium ions (K⁺) may move to a deeper depth of thesecond window member 100-S2 from the surface than that in the firstwindow member 100-S1. Accordingly, the depth of compression of thesecond window member 100-S2 may be larger than the depth of compressionof the first window member 100-S1. The depth of compression of thesecond window member 100-S2 may exert influence on the depth ofcompression of the window member 100 described later.

For example, the stress relief operation S200 may include a heattreatment operation. The heat treatment operation may be performed at atemperature of about 500° C. or above. As the temperature increases, atime during which the first window member 100-S1 is exposed to a heatsource may be shortened.

In this case, the stress relief operation S200 may further include asalt treatment operation. The salt treatment operation may be performedat substantially the same time as the heat treatment operation. Forexample, the heat treatment operation may be performed while the firstwindow member 100-S1 is exposed to a liquid salt.

The liquid salt may be a mixed salt in which a salt containing thepotassium ions is mixed with a salt containing the sodium ions. Thestress relief operation S200 may form the second window member 100-S2having various durabilities by controlling a mixing ratio of the mixedsalt. For example, when the mixing ratio of the salt containing thesodium ions increases, the second window member 100-S2 having therelatively high surface compressive stress may be formed. However, thestress relief operation S200 may be performed through various methodsand should not be limited to any one embodiment.

Then, as shown in FIG. 4 , the second reinforcement operation S300 maybe performed. The second reinforcement operation S300 may correspond toFIGS. 5F and 5G. The second reinforcement operation S300 may be anoperation that performs an ion-exchange treatment on the second windowmember 100-S2 to reinforce the second window member 100-S2. The initialwindow member 100 (hereinafter, referred to as a “window member”), whichis second-reinforcement treated, may correspond to the window member 100shown in FIG. 1A.

For example, the ion salt is provided to the second window member 100-S2to form the window member 100. The ion salt may be ions substituted forthe sodium ions (Na⁺) distributed in the medium MD.

For example, the ion salt may include the potassium ions (K⁺). The ionsalt provided to the second window member 100-S2 in the secondreinforcement operation S300 may be different from the ion salt providedto the initial window member 100-I in the first reinforcement operationS100.

The ion salt may be provided to the second window member 100-S2 throughvarious methods in the second reinforcement operation S300. For example,the ion salt may be provided by using a single salt. For example, thepotassium ions (K⁺) may be provided to the second window member 100-S2using potassium nitrate (KNO₃). However, the ion salt in the secondreinforcement operation S300 may be provided as the mixed salt andshould not be limited to any one embodiment.

As shown in FIG. 5G, the window member 100 includes the potassium ions(K⁺) disposed therein. The window member 100 may include the sodium ions(Na⁺) that are not substituted for the potassium ions (K⁺).

The window member 100 has the surface compressive stress higher than thesurface compressive stress of the second window member 100-S2 by thesecond reinforcement operation S300. The surface compressive stresshigher than the surface compressive stress of the second window member100-S2 may be provided by the potassium ions (K⁺) injected in the secondreinforcement operation S300.

The surface compressive stress of the window member 100, according toexemplary embodiments of the present disclosure, may be higher than thesurface compressive stress of the first window member 100-S1. The firstwindow member 100-S1, after the stress relief operation S200, may allowthe ion salts provided from an external source to be more easilyinjected thereto than the initial window member 100-I. The windowmember, 100 according to exemplary embodiments of the presentdisclosure, has more ability to accommodate surface compressive stressthan the first window member 100-S1, and thus the window member 100 maybe durable against external impacts and have increased reliability.

According to exemplary embodiments of the present disclosure, the windowmember 100 may have various sizes as long as the window member has thesurface compressive stress higher than the surface compressive stress ofthe second window member.

FIG. 6 is a graph illustrating a variation in stress of a window memberaccording to exemplary embodiments of the present disclosure. FIG. 6shows a graph PL-ES representing a variation in compressive stress as afunction of a depth of a window member 100 according to an exemplaryembodiment of the present disclosure and a graph PL-RS representing avariation in compressive stress as a function of a depth of a windowmember according to a comparative embodiment.

For the convenience of explanation, a cross-section of the window member100 and graphs PL-ES and PL-RS are shown together, and the graph PL-RSof the comparative embodiment is indicated by a dotted line, and thegraph PL-ES of the present disclosure is indicated by a solid line. Thewindow member 100 may correspond to the window member 100 shown in FIG.1B. Hereinafter, the variation in stress of the window member will bedescribed in detail with reference to FIG. 6 .

The compressive stress appearing in the window member 100 may be changeddepending on the depth. In this case, the depth indicates a distance ina depth direction toward an inner side of the window member 100 from asurface of the window member 100, and the depth direction may correspondto a direction toward the inner side of the window member 100 along adirection substantially parallel to the first direction DR1 from thefirst surface US and the second surface LS facing the first surface USin the first direction DR1.

Accordingly, the depth may be defined to be bilaterally symmetrical withreference to a line extending along the third direction DR3 and crossinga point corresponding to a half of the thickness of the window member100. A center line that is a reference line of the bilateral symmetrymay correspond to the center line CTR shown in FIG. 5D.

The window member 100 may have a first surface compressive stress CS onthe first surface US and the second surface LS. In FIG. 6 , thecompressive stress on the first surface US is substantially the same asthe compressive stress on the second surface LS, but the compressivestress on the first surface US may be different from the compressivestress on the second surface LS.

The window member 100 may have a first depth of compression DL. Asdescribed above, the first depth of compression DL may correspond to adepth at which the compressive stress becomes zero (0).

The window member 100 may have different stresses from each other aroundthe first depth of compression DL. The window member 100 may have thecompressive stress at a depth smaller than the first depth ofcompression DL and a tension at a depth greater than the first depth ofcompression DL.

The tension may be an inner tension formed against the compressivestress. Since the window member 100 forms the tension against thecompressive stress, a deformation of the window member 100 caused by thecompressive stress may be reduced, and the stress may be balanced. Forexample, the tension is shown as a negative compressive stress.

The window member 100 may have a first central tension CT at a depthgreater than the first depth of compression DL. For the convenience ofexplanation, the first central tension CT is shown to have a constantvalue in a range of the depth greater than the first depth ofcompression DL in FIG. 6 . However, according to some exemplaryembodiments of the present disclosure, the window member 100 may have atension that is variable in the range of the depth greater than thefirst depth of compression DL, and in this case, the first centraltension CT may be defined as an average value of tensions in the rangeof the depth greater than the first depth of compression DL.

For example, an area formed by the graph PL-ES of the present disclosurein the range of the first depth of compression DL may be substantiallythe same as an area formed by the graph PL-ES of the present disclosurein the range of the depth greater than the first depth of compressionDL. For example, a sum of a first area A1 defined by the compressivestress in the range of the first depth of compression DL from the secondsurface LS and a second area A2 defined by the compressive stress in therange of the first depth of compression DL from the first surface US maybe substantially the same as a third area A3 defined by the tension inthe range of depth greater than the first depth of compression DL.

The window member 100, according to exemplary embodiments of the presentdisclosure, forms the graph PL-ES defining the third area A3 defined bythe tension such that the third area A3 is the same as the sum of thefirst and second areas A1 and A2 defined by the compressive stress, andthus the window member 100 may be prevented from being damaged due tothe compressive stress during the reinforcement operation. Accordingly,the reinforcement operation may be performed on the window member 100,and the window member 100 may have increased durability.

When compared to the graph PL-RS of the comparative embodiment, thefirst surface compressive stress CS of the window member 100 may belower than the surface compressive stress CS-R of the comparativeembodiment. The first depth of compression DL of the window member 100may be greater than the depth of compression DL-R of the comparativeembodiment.

Accordingly, when the graph PL-ES of the present disclosure is comparedto the graph PL-RS of the comparative embodiment, the slope of thevariation in the compressive stress may be lowered in the range of thefirst depth of the compression DL. When the first depth of compressionDL becomes greater than the depth of compression DL-R of the comparativeembodiment, the slope may be reduced, and the area defined by thecompressive stress in the range of the depth of compression may be morereduced than that in the graph PL-RS of the comparative embodiment.

Thus, an intensity of the tension required in the range of the depthequal to or greater than the first depth of compression DL may bereduced. For example, the first central tension CT in the presentdisclosure may be smaller than a central tension CT-R in the comparativeembodiment. Since the area defined by the compressive stress in therange of the depth of compression DL is reduced, the balance of thestress may be maintained even though the first central tension CT islow.

The increasing of the first depth of compression DL and the decreasingof the intensity of the first surface compressive stress CS may beachieved through the stress relief operation S200 (refer to FIG. 4 ).The manufacturing method of the window member, according to exemplaryembodiments of the present disclosure, further includes the stressrelief operation S200 to form the window member 100 having the highdepth of compression and the low central tension, and thus the windowmember having the increased durability may be formed.

FIGS. 7A and 7B are graphs illustrating a variation of a compressivestress as a function of a depth of a window member according to anexemplary embodiment of the present disclosure. FIGS. 7A and 7B show thevariation of the compressive stress as a function of the depth of eachresult formed by each operation of the manufacturing method of thewindow member according to an exemplary embodiment of the presentdisclosure.

For the convenience of explanation, FIG. 7A shows a first graph PL1-Arepresenting a variation in compressive stress as a function of a depthof the first window member 100-S1 (refer to FIG. 5C) and a second graphPL2-A representing a variation in compressive stress as a function of adepth of the second window member 100-S2 (refer to FIG. 5E), and FIG. 7Bshows a third graph PL3-A representing a variation in compressive stressas a function of a depth of the window member 100 (refer to FIG. 5G).Hereinafter, the window member 100 according to the exemplary embodimentof the present disclosure will be described in detail with reference toFIGS. 7A and 7B.

Referring to FIG. 7A, the first graph PL1-A shows a distribution of thecompressive stress of the first window member 100-S1 formed through thefirst reinforcement operation S100 (refer to FIG. 4 ). For example, thefirst reinforcement operation S100 is performed by exposing the initialwindow member 100-I (refer to FIG. 5A) to a mixed salt, which isobtained by mixing the sodium nitrate (NaNO₃) with the potassium nitrate(KNO₃) in 3:7 ratio, at a temperature of about 530° C. during about fourhours. Accordingly, referring to the first graph PL1-A, the first windowmember 100-S1 may have a first surface compressive stress CS1-A and afirst depth of compression DL1-A.

As shown in FIG. 7A, the second graph PL2-A shows a distribution of thecompressive stress of the second window member 100-S2 formed through thestress relief operation S200 (refer to FIG. 4 ). For example, the stressrelief operation S200 is performed by heat-treating the first windowmember 100-S1 at a temperature of about 530° C. during about 120minutes.

Accordingly, referring to the second graph PL2-A, the second windowmember 100-S2 may have a second surface compressive stress CS2-A and asecond depth of compression DL2-A. In this case, the second surfacecompressive stress CS2-A is measured at about 200 MPa or below.

Referring to the first graph PL1-A and the second graph PL2-A, the firstsurface compressive stress CS1-A decreases to the second surfacecompressive stress CS2-A through the stress relief operation S200. Thestress relief operation S200 relieves the surface compressive stress ofthe corresponding member.

The second surface compressive stress CS2-A according to the exemplaryembodiment of the present disclosure may be smaller than about 150Mpa.According to the manufacturing method of the window member, thecompressive stress occurring on the surface is relieved through thestress relief operation S200, and thus a surface residual stress formedthrough the first reinforcement operation S100 may be distributed.

In addition, referring to the first graph PL1-A and the second graphPL2-A, the first depth of compression DL1-A increases to the seconddepth of compression DL2-A through the stress relief operation S200. Thestress relief operation S200 may increase the depth of compression ofthe corresponding member.

According to the manufacturing method of the window member, the ionsgenerating the compressive stress move to be adjacent to the centerportion through the stress relief operation S200, and thus the depth ofcompression may be controlled to be increased. The depth of compressionmay correspond to a depth of the compressive stress layer.

As shown in FIG. 7B, a third graph PL3-A shows a distribution of thecompressive stress of the window member 100 formed through the secondreinforcement operation S300 (refer to FIG. 4 ). For example, the secondreinforcement operation S300 is performed by exposing the second windowmember 100-S2 to a single salt of the potassium nitrate (KNO₃) at atemperature of about 420° C. during about thirty minutes. Accordingly,referring to the third graph PL3-A, the window member 100 may have athird surface compressive stress CS3-A and a third depth of compressionDL3-A.

Referring to the second graph PL2-A and the third graph PL3-A, thesecond surface compressive stress CS2-A increases to the third surfacecompressive stress CS3-A through the second reinforcement operationS300. The second reinforcement operation S300 provides the potassiumions that provide the surface compressive stress of the window member100.

In this case, the third surface compressive stress CS3-A is measured atabout 800 MPa. The third surface compressive stress CS3-Ahas a valuegreater than the first surface compressive stress CS1-A measured atabout 300 MPa.

According to the manufacturing method of the window member, since thesecond reinforcement operation S300 is performed after the stress reliefoperation S200, the window member may have more ability to accommodatesurface compressive stress than when only the first reinforcementoperation S100 is performed. Accordingly, the window member 100according to the exemplary embodiment of the present disclosure may haveincreased durability against external impacts and damages.

Referring to FIG. 7B, the third graph PL3-A may be divided into a firstsection and a second section in a range of depth equal to or smallerthan the third depth of compression DL3-A. The first section is a depthsection adjacent to the surface, and the variation of the compressivestress according to the depth appears relatively large when comparedwith the first graph PL1-A after the first reinforcement operation.

The second section is a depth section adjacent to the third depth ofcompression DL3-A, and the variation of the compressive stress accordingto the depth appears relatively small when compared with the first graphPL1-A after the first reinforcement operation.

In this case, the third graph PL3-A may include a point at which anabsolute value of the slope is smaller than about 2 MPa/µm in the secondsection. For example, a first slope SL1-A shown in FIG. 7B has a valueof about -0.6 MPa/µm. For example, the window member 100 according tothe exemplary embodiment of the present disclosure may have a graph ofdepth of compression-compressive stress, which has the slope smallerthan the absolute value of 2 in the range of the third depth ofcompression DL3-A.

For example, the third graph PL3-A may include a point at which theslope is about 0 MPa/µm in the second section. For example, in thewindow member 100 according to the exemplary embodiment of the presentdisclosure, a section in which no variation in the compressive stressexists along a direction to which the depth increases may exist.

This means that a graph including a section in which the compressivestress is changed in a gradual manner in the window member 100 mayoccur. This result may be caused by the stress relief operation S200 inwhich the potassium ions providing the compressive stress move to thecenter portion and the compressive stress moves to the center portionfrom the surface.

For example, the third graph PL3-A may include a point at which theslope is about 0 MPa/µm in the second section. Accordingly, the thirdgraph PL3-A may have a peak point PK-A that is convex upward. The peakpoint PK-A may exist in the range of the third depth of compressionDL3-A, and the peak point PK-A may be a point that is convex to thedirection in which the compressive stress increases.

According to other embodiments, the third graph PL3-A according to theexemplary embodiment of the present disclosure may have various shapesas long as the third graph PL3-A has the point at which the absolutevalue of the slope in the second section is smaller than about 2 MPa/µm.

In addition, referring to the first graph PL1-A and the second graphPL2-A, the first depth of compression DL1-A increases to the seconddepth of compression DL2-A through the stress relief operation S200. Thestress relief operation S200 may increase the depth of compression ofthe corresponding member.

As the depth of compression increases, a surface hardness of the windowmember 100 may be increased. Accordingly, an elasticity of the windowmember 100 may be increased against external impacts, and a crackoccurring on an outer portion of the window member 100 may be preventedfrom being propagated.

The manufacturing method of the window member 100 according to theexemplary embodiment of the present disclosure further includes thestress relief operation, and thus the slope of the variation of thecompressive stress according to the depth in the second reinforcementoperation may be finely controlled. Accordingly, although the depth ofcompression is high, the central tension may be prevented fromincreasing by reducing the slope of the variation in compressive stressaccording to the depth.

The increase of the central tension accelerates scattering of the windowmember due to external impacts. According to the present disclosure, thescattering of the window member may be prevented from increasing eventhough the external impacts are applied to the window member. Accordingto the exemplary embodiment, the window member having the thin thicknessmay be reinforced, and thus the thin-type window member may haveincreased durability.

FIGS. 8A and 8B are graphs illustrating a variation of a compressivestress as a function of a depth of a window member according to anexemplary embodiment of the present disclosure. FIGS. 8A and 8B show thevariation of the compressive stress as a function of the depth of eachresult formed by each operation of the manufacturing method of thewindow member according to the exemplary embodiment of the presentdisclosure.

For the convenience of explanation, FIG. 8A shows a first graph PL1-Srepresenting a variation in compressive stress as a function of a depthof the first window member 100-S1 (refer to FIG. 5C) and a second graphPL2-S representing a variation in compressive stress as a function of adepth of the second window member 100-S2 (refer to FIG. 5E), and FIG. 8Bshows a third graph PL3-S representing a variation in compressive stressas a function of a depth of the window member 100 (refer to FIG. 5G).

FIGS. 8A and 8B show graphs related to the second window member 100-S2formed by proceeding the stress relief operation S200 (refer to FIG. 4 )with a salt treatment. Hereinafter, the window member 100 according tothe exemplary embodiment of the present disclosure will be described indetail with reference to FIGS. 8A and 8B. In following description, tothe extent that description is omitted, it may be assumed that theomitted description is at least similar to that of the correspondingelements already discussed with respect to FIGS. 7A and 7B.

For example, the stress relief operation S200 may include an operationthat heat-treats the first window member 100-S1 (refer to FIG. 5C) byexposing the first window member 100-S1 to the molten salt. The moltensalt may include a mixed salt. For example, the molten salt may be asalt obtained by mixing the sodium nitrate (NaNO₃) with the potassiumnitrate (KNO₃). In this case, the mixed salt may be obtained by mixingthe sodium nitrate (NaNO₃) with the potassium nitrate (KNO₃) in a ratiodifferent from that in the first reinforcement operation S100 (refer toFIG. 4 ).

As shown in FIG. 8A, the graph PL1-S of the first window member to whichthe first reinforcement operation is applied is changed to the graphPL2-S of the second window member through the stress relief operationS200. In this case, the surface compressive stress may decrease to asecond surface compressive stress CS2-S from the first surfacecompressive stress CS1-S, and the depth of compression may increase to asecond depth of compression DL2-S from a first depth of compressionDL1-S.

As shown in FIG. 8B, the graph PL3-S of the window member to which thesecond reinforcement operation is applied is changed to have a thirdsurface compressive stress CS3-S from the second surface compressivestress CS2-S. The third surface compressive stress CS3-S may be greaterthan the second surface compressive stress CS2-S.

The graph PL3-S of the window member to which the second reinforcementoperation is applied has a third depth of compression DL3-S. The thirddepth of compression DL3-S may be higher than the first depth ofcompression DL1-S.

In this case, the graph PL3-S of the window member to which the secondreinforcement operation is applied may be divided into a first sectionin which the graph PL3-S has a slope value generally greater than thatof the graph PL1-S of the first window member 100-S1 to which the firstreinforcement operation is applied and a second section in which thegraph PL3-S has a slope value generally smaller than that of the graphPL1-S of the first window member 100-S1 to which the first reinforcementoperation is applied in the range of depth equal to or smaller than thethird depth of compression DL3-S. According to the manufacturing methodof the window member, since the stress relief operation is additionallyperformed, the graph in which the compressive stress varies depending onthe depth of the window member and the section with a varying slope isincluded is obtained.

The graph PL3-S of the window member to which the second reinforcementoperation is applied may include a point at which an absolute value ofthe slope is smaller than about 2 MPa/µm in the second section. Forexample, an absolute value of a slope of each of a first slope SL1-S anda second slope SL2-S is smaller than about 2 MPa/µm .

The graph PL3-S of the window member to which the second reinforcementoperation is applied may include a point at which an absolute value ofthe slope is equal to or greater than about 0 MPa/µm in the secondsection. Accordingly, the graph PL3-S of the window member to which thesecond reinforcement operation is applied may include a straight-linesection substantially parallel to a horizontal axis in the secondsection or a section that is convex upward. For example, a peak pointPK-S shown in FIG. 8B appears as the graph PL3-S of the window member towhich the second reinforcement operation is applied has a convex shape.

The manufacturing method of the window member according to the exemplaryembodiment of the present disclosure further includes the stress reliefoperation, and thus the graph of the compressive stress according to thedepth may be finely controlled. Therefore, although the depth of thecompressive stress increases in the window member having the thinthickness, the central tension may be prevented from increasing byrelieving the slope, and thus the window member may have the increaseddurability.

FIGS. 9A and 9B are graphs illustrating a variation of an ionconcentration as a function of a depth of a window member according toan exemplary embodiment of the present disclosure. FIGS. 9A and 9B showthe variation of the ion concentration as a function of the depth ofeach result formed by each operation of the manufacturing method of thewindow member according to the exemplary embodiment of the presentdisclosure.

The ion concentration variation shown in FIGS. 9A and 9B may be avariation in concentration of the potassium ions (K⁺). For theconvenience of explanation, FIG. 9A shows a first graph PL1-IArepresenting the ion concentration variation as a function of the depthof the first window member 100-S1 (refer to FIG. 5C) and a second graphPL2-IA representing the ion concentration variation as a function of thedepth of the second window member 100-S2 (refer to FIG. 5E), and FIG. 9Bshows a third graph PL3-IA representing the ion concentration variationas a function of the depth of the window member 100 (refer to FIG. 5G).

For example, the second window member 100-S2 may be formed by using theheat treatment as the stress relief operation S200 (refer to FIG. 4 ).Accordingly, FIGS. 9A and 9B show the ion concentration variation withrespect to FIGS. 7A and 7B, respectively.

Hereinafter, the window member 100 according to the exemplary embodimentof the present disclosure will be described in detail with reference toFIGS. 9A and 9B. In following description, to the extent thatdescription is omitted, it may be assumed that the omitted descriptionis at least similar to that of the corresponding elements alreadydiscussed with respect to FIGS. 7A, 7B, 8A, and 8B.

Referring to FIG. 9A, the graph PL1-IA of the first window member towhich the first reinforcement operation is applied is changed to thegraph PL2-IA of the second window member through the stress reliefoperation S200. In this case, a surface concentration of the potassiumions (K⁺) appears to be more reduced in the graph PL2-IA of the secondwindow member than that in the graph PL1-IA of the first window member.

As described above, the potassium ions (K⁺) injected into the firstwindow member 100-S1 move in the stress relief operation S200. Thepotassium ions (K⁺) existing adjacent to the surface of the first windowmember 100-S1 move to the center portion of the first window member100-S1 through the stress relief operation S200. Accordingly, the ionconcentration in the surface is reduced.

Referring to FIG. 9A, the graph PL1-IA of the first window membercrosses the graph PL2-IA of the second window member at a depth of afirst point D1. The ion concentration of the potassium ions (K⁺) at thedepth equal to or greater than first point D1 is higher in the graphPL2-IA of the second window member than that in the graph PL1-IA of thefirst window member. This may mean that the potassium ions (K⁺) move tobe adj acent to the center portion of the first window member 100-S1through the stress relief operation S200.

As shown in FIG. 9B, the graph PL3-IA of the window member to which thesecond reinforcement operation is applied has the surface ionconcentration higher than that of the graph PL2-IA of the second windowmember. This may be considered as a variation caused by the potassiumions (K⁺) additionally injected through the second reinforcementoperation S300.

Referring to FIG. 9B, when compared to the graph PL1-IA of the firstwindow member, the graph PL3-IA of the window member to which the secondreinforcement operation is applied may be divided into a section inwhich a slope of the concentration variation is relatively large and asection in which the slope of the concentration variation is relativelysmall. The section in which the slope of the concentration variation isrelatively small has the slope close to zero (0).

As described above, the potassium ions (K⁺) may correspond to a sourceproviding the compressive stress, and the position and concentrationvariation of the potassium ions (K⁺) may be related to the distributionof the compressive stress of the corresponding member. The window memberaccording to the exemplary embodiment of the present disclosure furtherincludes the stress relief operation, the concentration distribution ofthe potassium ions (K⁺) may be controlled to have a distribution with asteep slope in the section adjacent to the surface and a gentle slope inthe section adjacent to the center portion.

Accordingly, although the potassium ions (K⁺) reach a depth adjacent tothe center portion, the central tension may be prevented fromincreasing, and thus the durability of the window member may beincreased.

FIGS. 10A and 10B are graphs illustrating a variation of an ionconcentration as a function of a depth of a window member according toan exemplary embodiment of the present disclosure. FIGS. 10A and 10Bshow the variation of the ion concentration as a function of the depthof each result formed by each operation of the manufacturing method ofthe window member according to the exemplary embodiment of the presentdisclosure.

The ion concentration variation shown in FIGS. 10A and 10B may be avariation in concentration of the potassium ions (K⁺). For theconvenience of explanation, FIG. 10A shows a first graph PL1-ISrepresenting the ion concentration variation as a function of the depthof the first window member 100-S1 (refer to FIG. 5C) and a second graphPL2-IS representing the ion concentration variation as a function of thedepth of the second window member 100-S2 (refer to FIG. 5E), and FIG.10B shows a third graph PL3-IS representing the ion concentrationvariation as a function of the depth of the window member 100 (refer toFIG. 5G).

For example, the second window member 100-S2 may be formed by using thesalt treatment as the stress relief operation S200 (refer to FIG. 4 ).Accordingly, FIGS. 10A and 10B show the ion concentration variation withrespect to FIGS. 8A and 8B, respectively.

Hereinafter, the window member 100 according to the exemplary embodimentof the present disclosure will be described in detail with reference toFIGS. 10A and 10B. In following description, to the extent thatdescription is omitted, it may be assumed that the omitted descriptionis at least similar to that of the corresponding elements alreadydiscussed with respect to FIGS. 9A and 9B.

Referring to FIG. 10A, the graph PL1-IS of the first window member towhich the first reinforcement operation is applied is changed to thegraph PL2-IS of the second window member through the stress reliefoperation S200. In this case, a surface concentration of the potassiumions (K⁺) appears to be reduced more in the graph PL2-IS of the secondwindow member than that in the graph PL1-IS of the first window member.

As described above, the potassium ions (K⁺) injected into the firstwindow member 100-S1 move in the stress relief operation S200. Thepotassium ions (K⁺) existing adjacent to the surface of the first windowmember 100-S1 move to the center portion of the first window member100-S1 through the stress relief operation S200. Accordingly, the ionconcentration in the surface is reduced.

Referring to FIG. 10A, the graph PL1-IS of the first window membercrosses the graph PL2-IS of the second window member at a depth of asecond point D2. The ion concentration of the potassium ions (K⁺) at thedepth equal to or greater than second point D2 is higher in the graphPL2-IS of the second window member than that in the graph PL1-IS of thefirst window member. As described above, this means that the potassiumions (K⁺) move to be adjacent to the center portion of the first windowmember 100-S1 through the stress relief operation S200.

Referring to FIGS. 9A and 10A, the surface ion concentration of thegraph PL2-IS of the second window member may appear to be lower than thesurface ion concentration of the graph PL2-IA of the second windowmember shown in FIG. 9A, and an upward convex shape may appear beforethe second point D2.

When the stress relief operation S200 further includes the salttreatment operation, the stress relief operation S200 may exert a largerinfluence on the movement of the potassium ions (K⁺) than that when thestress relief operation S200 includes only the heat treatment operation.Accordingly, more rapid variation in ion concentration may be observedin the graph PL2-IA of FIG. 10A, to which the slat treatment is applied,than that in the graph PL2-IA of FIG. 9A.

As shown in FIG. 10B, the graph PL3-IS of the window member to which thesecond reinforcement operation S300 is applied has the more increasedsurface ion concentration than that of the graph PL2-IS of the secondwindow member. This may be considered as a variation by the potassiumions (K⁺) additionally injected into the window member through thesecond reinforcement operation S300.

Referring to FIG. 10B, when compared to the graph PL1-IS of the firstwindow member, the graph PL3-IS of the window member to which the secondreinforcement operation S300 is applied is divided into a section inwhich a slope of the concentration variation is relatively large and asection in which the slope of the concentration variation is relativelysmall. Detailed descriptions on the above are as shown in FIGS. 10A and10B.

The manufacturing method of the window member according to the exemplaryembodiment of the present disclosure further includes the stress reliefoperation that performs the salt treatment with the heat treatment, andthus a mobility of the ions injected into the window member may beincreased. Accordingly, the durability of the window member may beincreased, and the reinforcement process may be carried out.

FIG. 11A is a flowchart illustrating a method of manufacturing a windowmember according to an exemplary embodiment of the present disclosure,and FIG. 11B is a flowchart illustrating a portion of the method ofmanufacturing the window member of FIG. 11A.

Referring to FIG. 11A, the method of manufacturing the window memberaccording to the exemplary embodiment of the present disclosure mayinclude a first reinforcement operation S1000 and a second reinforcementoperation S2000. As shown in FIG. 11A, the stress relief operation S200shown in FIG. 4 may be omitted from the method of manufacturing thewindow member. For example, the window member according to the presentdisclosure may be manufactured through two times reinforcementoperation. Hereinafter, the method of manufacturing the window memberaccording to exemplary embodiments of the present disclosure will bedescribed in detail with reference to FIGS. 11A and 11B.

The first reinforcement operation S1000 reinforces an initial windowmember. Referring to FIGS. 11A and 11B, the first reinforcementoperation S1000 may include an ion exchange operation S1100 and analkalinity control operation S1200.

The ion exchange operation S1100 provides a first reinforcementenvironment to the initial window member. The first reinforcementenvironment includes an ion exchange environment that includes atemperature condition at high temperature equal to or higher than about500° C. and first ion salts.

The ion exchange operation S1100 may substantially correspond to thefirst reinforcement operation S100 shown in FIG. 4 . Accordingly, thefirst reinforcement environment may include the ion exchange environmentthat includes the temperature condition with a temperature range ofabout ±20° C. with respect to a temperature lower than a distortionpoint of the initial window member by about 50° C. and potassium ionsalts. Accordingly, a predetermined compressive stress may occur on asurface of the window member that is first reinforced. To the extentthat description is omitted, it may be assumed that the omitteddescription is at least similar to that of the corresponding elementsalready discussed.

The alkalinity control operation S1200 controls an alkalinity in theenvironment of the first reinforcement operation S1000. The alkalinitycontrol operation S1200 may start after the ion exchange operation S1100starts or may start together with the ion exchange operation S1100.

The alkalinity control operation S1200 may be a step to provide anadditive in the first reinforcement operation S1000 to alleviate thealkalinity. Accordingly, the alkalinity control operation S1200 mayalleviate the alkalinity of the first reinforcement environment. Forexample, a concentration of some salts in the first reinforcementenvironment may increase as the ion exchange operation S1100 proceeds.

For example, the ion exchange environment of the first reinforcementenvironment may include a liquid solution including a mixed salt. As anexample, in the case that the ion exchange environment of the firstreinforcement environment includes the mixed salt in the liquid stateincluding a potassium ion salt and a carbonate ion salt, the potassiumion salt infiltrates into the initial window member while the ionexchange operation proceeds, and thus a relative concentration of thecarbonate ion salt in the mixed salt may increase. Accordingly, thealkalinity may gradually increase in the first reinforcementenvironment. In this case, the additive provided in the alkalinitycontrol operation S 1200 reacts with the carbonate ion salt remaining inthe alkalinity control operation S1200, and thus the alkalinity of thefirst reinforcement environment may gradually decrease.

The additive may include various materials to alleviate the alkalinity.As an example, the additive may include a chemically stable oxidematerial, such as an acidic oxide material or an amphoteric oxidematerial. For example, the additive may include B2O3, SiO2, Al2O3, SnO2,or a combination thereof.

For example, the additive may include a silicon nitride-based material.The additive controls the alkalinity of the first reinforcementenvironment but does not react with the initial window member.

The additive may be provided in small amount in the alkalinity controloperation S1200 according to exemplary embodiments of the presentdisclosure. As an example, the additive may be provided in a ratio equalto or greater than about 0.1% and equal to or smaller than about 1% tothe mixed salt in the liquid state of the first reinforcementenvironment.

As described above, when the alkalinity of the first reinforcementoperation S1000 is alleviated, the window member may be more resistantto corrosion. This will be described later.

Referring to FIG. 11A, the second reinforcement operation S2000 may beperformed. In this case, the reinforced window member may proceed to thesecond reinforcement operation S2000 without going through an additionalstress relief operation. Accordingly, the manufacturing method of thewindow member may be simplified, and the manufacturing cost of thewindow member may be reduced. However, according to some exemplaryembodiment of the present disclosure, the stress relief operation may befurther performed before entering the second reinforcement operationS2000, and thus reliability of the window member may be increased.However, the manufacturing method of the window member, according to thepresent invention, is not be limited to the examples described herein.

The second reinforcement operation S2000 may include an ion exchangeoperation. The second reinforcement operation S2000 may correspond tothe second reinforcement operation S300 shown in FIG. 4 . The secondreinforcement operation S2000 may be substantially the same aspreviously described with respect to FIG. 4 .

The manufacturing method of the window member further includes thealkalinity control operation, and thus the window member havingincreased reliability may be manufactured.

FIG. 12 is a graph illustrating a compressive stress as a function of adepth of a window member according to an exemplary embodiment of thepresent disclosure. For the convenience of explanation, FIG. 12 includesthe graph illustrating the compressive stress as a function of the depthof the window member that is reinforced through the first reinforcementoperation shown in FIG. 11A. In addition, for the convenience ofexplanation, FIG. 12 shows a first graph PL-C1 and a second graph PL-C2.

The first graph PL-C1 may show the compressive stress as a function ofthe depth of the window member to which only the ion exchange operationS1100 of the first reinforcement operation S1000 is applied.Accordingly, the first graph PL-C1 may correspond to the compressivestress graph of the first window member 100-S1 shown in FIG. 5C.

The second graph PL-C2 may correspond to the compressive stress graph ofthe window member to which both the ion exchange operation S1100 and thealkalinity control operation S 1200 of the first reinforcement operationS1000 are applied. For example, since the ion exchange operation S1100is further performed on the window member, according to exemplaryembodiments of the present disclosure, in the first reinforcementoperation S1000, the window member may have a compressive stressbehavior changed to the second graph PL-C2 from the first graph PL-C1.

For the convenience of explanation, FIG. 12 shows schematic graphshaving average slopes corresponding to those shown in FIG. 6 .Hereinafter, the manufacturing method of the window member according toexemplary embodiments of the present disclosure will be described indetail with reference to FIG. 12 .

As shown in FIG. 12 , the first graph PL-C1 has a surface compressivestress CS at a point at which a depth is zero (0) and has a compressivestress depth DL when the compressive stress is zero (0). In this case,the average slope of the first graph PL-C1 depending on the increase ofthe depth from the surface may correspond to the surface compressivestress CS with respect to the compressive stress depth DL.

The second graph PL-C2 has the same surface compressive stress CS andthe same compressive stress depth DL as those of the first graph PL-C1,but it should not be limited thereto or thereby. For example, avariation may occur on at least one of the surface compressive stress CSand the compressive stress depth DL since the alkalinity controloperation S 1200 is performed on the window member, but the presentinvention is not limited thereto.

The second graph PL-C2 has a transition point TP. The transition pointTP may indicate a point at which the slope is abruptly changed. Thesecond graph PL-C2 includes a first plot S1 having a first slope and asecond plot S2 having a second slope with respect to the transitionpoint TP.

The first plot S1 shows a compressive stress behavior in a depth rangefrom the surface with a depth of zero (0) to the transition point TP.The first plot S1 is shown in a form of a straight line having theaverage slope. For example, the first plot S1 may have the average slopequal to or greater than about 200 MPa/µm and equal to or smaller thanabout -40 MPa/µm.

An absolute value of the average slope of the first plot S1 may begreater than an absolute value of the average slope of the first graphPL-C1. For example, the compressive stress in the depth range equal toor smaller than the transition point TP may be largely reduced comparedwith the surface compressive stress CS occurring on the surface as thedepth increases.

Since the second graph PL-C2 includes the first plot S1, the secondgraph PL-C2 may have relatively low compressive stress when comparedwith the first graph PL-C1. According to the present disclosure, thecompressive stress in an area adjacent to the surface may be relievedthrough the alkalinity control operation. Accordingly, the window membermay be more resistant to corrosion, which may occur in processing, bycontrolling the compressive stress in the depth adjacent to the surfaceduring the first reinforcement operation, and thus the reliability ofthe window member may be increased.

The second plot S2 shows a compressive stress behavior in a depth rangeequal to or greater than the transition point TP. An absolute value ofthe average slope of the second plot S2 may be smaller than the absolutevalue of the average slope of the first graph PL-C1. For example, thesecond plot S2 may have the average slop equal to or greater than about-8 MPa/µm and equal to or smaller than about -2 MPa/µm.

The compressive stress applied in the depth range equal to or greaterthan the transition point TP may be slightly reduced compared with thedepth range equal to or smaller than the transition point TP as thedepth increases.

In this case, according to the present disclosure, since the size of thecompressive stress applied to the point having the depth correspondingto the transition point TP is sufficiently lowered, the size of thecompressive stress may be low even though the compressive stress isreduced by a small slope in the depth equal to or greater than thetransition point TP. Accordingly, the compressive stress occurring inthe depth range equal to or greater than the transition point TP mayhave a relatively small size compared to the first graph PL-C1.

As described above, the compressive stress occurring in the windowmember that is first reinforced in the range of the compressive stressdepth DL from the surface may exert an influence on a central tensileforce applied to the window member that is first reinforced in the depthrange equal to or greater than the compressive stress depth DL. Forexample, an area occupied by the second graph PL-C2 is smaller than anarea occupied by the first graph PL-C1.

For example, according to the present disclosure, since themanufacturing method of the window member further includes thealkalinity control operation, the transition point TP may be generated,and thus the compressive stress behavior of the window member may becontrolled such that the window member has the low central tensile forceon the same surface compressive stress CS and the same compressivestress depth DL. Accordingly, the reliability of the window member inprocess and use may be increased.

FIG. 13 is a graph illustrating a compressive stress as a function of adepth of a window member according to an exemplary embodiment of thepresent disclosure. For the convenience of explanation, FIG. 13 shows areference graph PL-FN, a first graph PL-11, and a second graph PL-21. Inaddition, for the convenience of explanation, each of the referencegraph PL-FN, the first graph PL-11, and the second graph PL-21 is shownin a straight line with an average slope.

Referring to FIG. 13 , the reference graph PL-FN has a predeterminedsurface compressive stress CS, a predetermined compressive stress depthDL, and a predetermined average slope. The average slope of thereference graph PL-FN may be a ratio of the compressive stress depth DLto the surface compressive stress CS.

The first graph PL-11 may have a first transition point P1. The firstgraph PL-11 may be divided into two portions distinguished from eachother with respect to the first transition point P1 at which the averageslope is abruptly changed.

As described above, the first transition point P1 may be formed throughthe alkalinity control operation S1200 (refer to FIG. 12 ). The firstgraph PL-11 may have the average slope having an absolute value greaterthan an absolute value of the average slope of the reference graph PL-FNin a depth equal to or smaller than the first transition point P1 andhave the average slope having the absolute value smaller than theabsolute value of the average slope of the reference graph PL-FN in adepth equal to or greater than the first transition point P1.

The second graph PL-21 may have a second transition point P2. The secondgraph PL-21 may be divided into two portions distinguished from eachother with respect to the second transition point P2 at which theaverage slope is abruptly changed.

As described above, the second transition point P2 may be formed throughthe alkalinity control operation S1200. The second graph PL-21 may havethe average slope having an absolute value greater than the absolutevalue of the average slope of the reference graph PL-FN in a depth equalto or smaller than the second transition point P2 and have the averageslope having the absolute value smaller than the absolute value of theaverage slope of the reference graph PL-FN in a depth equal to orgreater than the second transition point P2.

As shown in FIG. 13 , the window member, according to exemplaryembodiments of the present disclosure, may be controlled such that thetransition point is formed at various depths. According to the presentdisclosure, the central tensile force of the window member may becontrolled by forming the transition point and controlling a position ofthe transition point while maintaining the surface compressive stress CSand the compressive stress depth DL.

In a case that the transition point of the window member moves to thesecond transition point P2 from the first transition point P1, thecentral tensile force of the window member may increase. However, thevariation of the compressive stress may be steadily changed to thetransition point.

In a case that the transition point of the window member moves to thefirst transition point P1 from the second transition point P2, thecentral tensile force of the window member may decrease. Accordingly,the window member may have high impact resistance.

The transition point of the window member, according to exemplaryembodiments of the present disclosure, may be greater than about 15 µm.Accordingly, although the window member has high surface compressivestress, the corrosion of the window member occurring during processes ordue to an external contamination or impact in use may be prevented.

When the transition point of the window member, according to exemplaryembodiments of the present disclosure, increases, the transition pointexerts an influence on the central tensile force of the window member.Accordingly, the transition point may be determined within a range wherethe central tensile force is not too large. As an example, in a windowmember having a thickness of about 0.8 mm and a limit central tensilestress of about 67 MPa, the transition point may be equal to or smallerthan about 30 µm. In the manufacturing method of the window member,according to exemplary embodiments of the present disclosure, thetransition point is formed within a range that increases a corrosionresistance with respect to the processes and has the stable centraltensile stress, and thus the reliability of the window member may beincreased.

FIGS. 14A and 14B are graphs illustrating a compressive stress as afunction of a depth of a window member according to an exemplaryembodiment of the present disclosure. FIGS. 14A and 14B show a referenceline RL crossing a point at which a depth is about 15 µm. Hereinafter,exemplary embodiments of the present disclosure will be described withreference to FIGS. 14A and 14B.

For the convenience of explanation, FIG. 14A shows first, second, third,and fourth graphs PL11, PL12, PL13, and PL14. The first, second, third,and fourth graphs PL11, PL12, PL13, and PL14 may be compressive stressgraphs of exemplary embodiments obtained by applying different timeconditions in the second reinforcement operation S2000 (refer to FIG.11A).

For example, the first graph PL11 indicates a first exemplary embodimentin which the second reinforcement operation S2000 is performed duringabout 30 minutes, the second graph PL12 indicates a second exemplaryembodiment in which the second reinforcement operation S2000 isperformed during about 60 minutes, the third graph PL13 indicates athird exemplary embodiment in which the second reinforcement operationS2000 is performed during about 90 minutes, and the fourth graph PL14indicates a fourth exemplary embodiment in which the secondreinforcement operation S2000 is performed during about 120 minutes.Other conditions applied to the first to fourth exemplary embodimentsmay be the same as each other except for the time conditions. Detailednumerical results with respect to each of the first, second, third, andfourth graphs PL11, PL12, PL13, and PL14 are shown in Table 1 below.

TABLE 1 Second reinforcement time First average slope Second averageslope Transition point First graph (PL11) 30 minutes -103 MPa/µm -1.8MPa/µm 9 µm Second graph (PL12) 60 minutes -80 MPa/µm -1.8 MPa/µm 12 µmThird graph (PL13) 90 minutes -68 MPa/µm -2.2 MPa/µm 15 µm Fourth graph(PL14) 120 minutes -54 MPa/µm -2.7ΜFa/µm 17 µm

As shown in Table 1, the first, second, third, and fourth graphs PL11,PL12, PL13, and PL14 may have different transition points TP (refer toFIG. 12 ) from each other by varying the second reinforcement time. Thefirst average slope, which is the average slope in the depth range equalto or smaller than the transition point TP, may correspond to theaverage slope of the first plot S1 shown in FIG. 12 . The second averageslope, which is the average slope in the depth range equal to or greaterthan the transition point TP, may correspond to the average slope of thesecond plot S2 shown in FIG. 12 .

Referring to Table 1, the fourth graph PL14 corresponding to the fourthexemplary embodiment has the transition point exceeding about 15 µm. Forexample, referring to FIG. 14A, the transition points of the first,second, and third graphs PL11, PL12, and PL13 with respect to thereference line RL exist at depths equal to or smaller than the referenceline RL. Accordingly, the window member according to the fourthexemplary embodiment may have the corrosion resistance that is higherthan those of the first to third exemplary embodiments, and the windowmember may be less vulnerable during processing.

According to the present disclosure, since a process time (duration) ofthe second reinforcement operation with respect to the same processcondition is controlled, the transition point may be controlled.Accordingly, the reliability of the window member may be increased bycontrolling a process time of a conventional process without addingseparate processes.

For the convenience of explanation, FIG. 14B shows fifth, sixth,seventh, and eighth graphs PL21, PL22, PL23, and PL24. The fifth, sixth,seventh, and eighth graphs PL21, PL22, PL23, and PL24 may be compressivestress graphs of exemplary embodiments obtained by applying differenttime conditions in the second reinforcement operation S2000 orcompressive stress graphs of exemplary embodiments to which the stressrelief operation S200 shown in FIG. 4 is applied.

For example, the fifth graph PL21 and the sixth graph PL22 may be graphsillustrating the compressive stress behavior of the embodimentsmanufactured by the manufacturing method to which the stress reliefoperation is added, and the seventh graph PL23 and the eighth graph PL24may be graphs illustrating the compressive stress behavior of theembodiments manufactured by the manufacturing method to which the stressrelief operation is not added.

The fifth graph PL21 relates to a fifth exemplary embodiment in whichthe second reinforcement operation S2000 is performed during about 30minutes after the stress relief operation S200, the sixth graph PL22relates to a sixth exemplary embodiment in which the secondreinforcement operation S2000 is performed during about 120 minutesafter the stress relief operation S200, the seventh graph PL23 relatesto a seventh exemplary embodiment in which the second reinforcementoperation S2000 is performed during about 60 minutes without applyingthe stress relief operation S200 after the first reinforcement operationS1000, and the eighth graph PL24 relates to an eighth exemplaryembodiment in which the second reinforcement operation S2000 isperformed during about 90 minutes without applying the stress reliefoperation S200 after the first reinforcement operation S1000.

For example, referring to FIG. 14B, the transition point of the fifthgraph PL21 with respect to the reference line RL exists at a depth equalto or smaller than the reference line RL, and the transition points ofthe sixth, seventh, and eighth graphs PL22, PL23, and PL24 exist atdepths exceeding the reference line RL. Accordingly, the window membersaccording to the sixth to eighth exemplary embodiments may have thecorrosion resistance higher than that of the fifth exemplary embodiment,and the window member may be less vulnerable during processing.

According to the present disclosure, the transition point may becontrolled by controlling the process time of the second reinforcementoperation with respect to the same process condition or the addition ofthe stress relief operation. As an example, referring to the fifth andsixth graphs PL21 and PL22, although the stress relief operation isfurther applied to the window member, the position of the transitionpoint may be changed by controlling the process time (duration) of thesecond reinforcement operation. In addition, referring to the seventhand eighth graphs PL23 and PL24, although the stress relief operation isnot further applied to the window member, the position of the transitionpoint may be controlled by controlling the process time (duration) ofthe second reinforcement operation.

In addition, referring to the sixth, seventh, and eighth graphs PL22,PL23, and PL24, in the case that the stress relief operation is notapplied to the window member, the process time (duration) of the secondreinforcement operation may be reduced to control the position of thetransition point.

According to the exemplary embodiment of the present disclosure, theposition of the transition point may be changed by controlling variousprocess conditions of the reinforcement operation, and thus thecompressive stress behavior of the window member may be controlled.

Although exemplary embodiments of the present invention have beendescribed herein with reference to the accompanying figures, it isunderstood that the present invention is not limited to these exemplaryembodiments but various changes and modifications can be made within thespirit and scope of the present disclosure.

What is claimed is:
 1. A window member, comprising: a base comprising afirst surface and a second surface facing the first surface in a firstdirection, the base having a thickness defined in the first direction;first ion salts distributed in the base and each of the first ion saltshaving a first ion radius; and second ion salts distributed in the baseand each of the second ion salts having a second ion radius greater thanthe first ion radius, wherein a variation in compressive stressaccording to a depth increasing along the first direction from the firstsurface of the base forms a first plot, and the first plot comprises apoint at which an absolute value of a slope is smaller than about 2MPa/µm in a depth range in which the compressive stress is greater thanabout 0 MPa/µm.
 2. The window member of claim 1, wherein the thicknessof the base is equal to or smaller than about 0.5 mm.
 3. The windowmember of claim 1, wherein the first plot has a first surfacecompressive stress at a point at which the depth is about 0 µm and acompressive stress of about OMPa at a point at which the depth is afirst depth of compression, the first plot is divided into a firstsection in which the absolute value of the slope is equal to or greaterthan about 2 MPa/µm and a second section in which the absolute value ofthe slope is smaller than about 2 MPa/µm in a range in which the depthis equal to or greater than about OMPa and equal to or smaller than thefirst depth of compression, and the second section is defined in a depthgreater than a depth in which the first section is defined.
 4. Thewindow member of claim 3, wherein the first plot comprises a point atwhich the slope is equal to or greater than about 0 MPa/µm in the secondsection.
 5. The window member of claim 4, wherein the first plot has anupward convex shape in the second section.
 6. The window member of claim1, wherein the first ion salts include sodium ions, and the second ionsalts include potassium ions.
 7. A window member, comprising: a firstsurface; and a second surface facing the first surface, the windowmember having a thickness defined in a first direction between the firstsurface and the second surface, the window member having a compressivestress smaller than about 150 MPa on the first surface, and having acompressive stress graph varied depending on a depth increasing alongthe first direction from the first surface, wherein the compressivestress graph comprises a first plot at a depth equal to or smaller thana transition point and a second plot at a depth greater than thetransition point, the first plot has an average slope equal to orgreater than about -200 MPa/µm and equal to or smaller than about -40MPa/µm, the second plot has an average slope different from the firstplot, and the transition point is greater than about 15 µm.
 8. Thewindow member of claim 7, wherein an absolute value of the average slopeof the second plot is smaller than an absolute value of the averageslope of the first plot.
 9. The window member of claim 8, wherein thesecond plot comprises a section having an average slope equal to orgreater than about -8 MPa/µm and equal to or smaller than about -2MPa/µm.
 10. The window member of claim 8, wherein a depth range in whichthe second plot is defined comprises a depth at which the compressivestress becomes zero.
 11. The window member of claim 7, wherein thethickness is equal to or smaller than about 0.8 mm.
 12. The windowmember of claim 11, wherein the compressive stress graph has thecompressive stress of zero when the depth is equal to or smaller thanabout 30 µm.
 13. The window member of claim 7, wherein the transitionpoint is equal to or smaller than about 30 µm.